When it comes to writing, dialogue is just one of the important elements scripts should have. As a writer myself, I understand how difficult writing dialogue is, and honestly, most professionals go through this as well. If you're unsure how to make your dialogue stronger, and perhaps more effective, take a look at some of the following tips below!
Give each character a distinct voice
Let's be honest, everyone has a different voice. When you go about your day, it's highly unlikely that two people sound the same or have the same personalities. When you're writing dialogue, it's important that no two characters sound alike. One thing to consider is giving each character a different personality. For example, notice how the characters in "Inside Out" Joy, Fear, Disgust, Anger, and Sadness have distinct personalities and their dialogue reflects it.
When a reader is going through your script, it's important that they can tell the difference between the characters. If they're certain that more than one character sounds the same, they could be easily drawn out of the script, and lose interest.
Show, don't tell
This is an important rule in screenwriting, and writers should keep this in mind. Instead of having a character speak what is on their mind, it's always a good idea to use subtext! Sure having on the nose dialogue once or twice in your script won't cause too much damage, but if you do it frequently, the reader could easily put your script to the side. If you're unsure if the dialogue is on the nose, consider reading it out loud to yourself and then ask, "Does this feel natural?" If yes, keep it. If not, try to reword it so the audience can "read between the lines".
Another thing the writer could consider asking themself is, "Is the dialogue necessary?" Before writing a scene, see if it's possible to have no dialogue whatsoever, after all actions do speak louder than words.
Once you're able to have a scene without dialogue, then you can determine if the characters in the scene should speak or not.
Why is it there?
That's the most important question writers should ask before putting in any dialogue. Does the dialogue drive the plot forward? What are we supposed to take away from their dialogue?
If you have a group of people sitting around the dinner table conversing, it has to serve a purpose to the scene. Sometimes, depending on the situation, audiences can become engaged with whatever the conversation is, but if it's just casual, then it'll feel like we're flies on a wall, observing people talking about whatever.
Get to the point!
Finally, when it comes to writing dialogue, it's important to get to their main point. As much as the audience would love to see someone perform a three-minute monologue, depending on the situation, it could be easily boring. However, if you must have the monologue, the writer might want to consider placing a brief line of action once every four to five lines or so before the character continues talking.
When I read for AFF, I noticed there was a lengthy scene where a character was reading a passage from a novel out loud to someone, and it went on for about three or so pages, with no action in between. Did it have anything to do with the plot? Kind of. Was it interesting? It's debatable, although I might've not been the target audience, it's hard to say if audiences would be able to stay tuned into the story or not.
So, when you're writing dialogue, please keep these tips in mind. If you're still unsure how people talk, consider people watching. As you go about your day, listen in on how people communicate with each other. What are they wearing? How do they move or speak? What expressions to they show? Without intruding on their conversation, see if you can read between the lines of the situation.